This laboratory has previously demonstrated a highly significant relationship between the incorporation of ara-C into DNA and the loss of clonogenic survival in a number of cell lines. It was shown that inhibition of DNA synthesis is proportional to the extent of (ara-C) DNA formation and is correlated with increasing proportion of ara-C residues at the chain terminus. The extent of (ara-C) DNA has been shown to be better than intracellular ara-CTP levels in correlation with cytotoxicity. The close relationship between (ara-C) DNA formation and cytotoxicity has recently been extended to nonreplicative DNA repair following UV light damage in growth arrested human fibroblasts. This work has improved our understanding of the molecular mechanisms of ara-C and will now be extended into clinical application. We now propose studying the pharmacokinetic variability of ara-c in very low dose infusions (20 mg/M2/day), standard doses (200-500 mg/M2/day) and very high dose infusions (6 gm/M2/day). We will use myeloblasts from leukemic patients to quantitate the extent of ara-C incorporation into DNA and the clonogenic survival following ara-C exposure, then correlate these pharmacologic measures with clinical measures of response. We will extend our studies into the interactions of established alkylating agents with ara-C and integrate the results of our phase I trial of continuous infusion high dose ara-C into new clinical trials of alkylating agents and ara-C in solid tumors. These goals involve a closely integrated program of in vitro work and clinical investigation. Plasma levels of ara-C will be measured by established HPLC or RIA assays. We will use myeloblasts from leukemia patients, MCF-7 breast cancer cells and growth arrested human fibroblasts for in vitro studies. The ara-C incorporation during replicative and repair DNA synthesis will be monitored by equilibrium centrifugation and clonogenic survival will be determined in tissue culture. DNA damage will be monitored using the alkaline elution method. These proposals extend our work on the pharmacodynamics of ara-C into biochemically rational clinical trials for the treatment of human malignancy.